1. Field of the Invention
The present invention relates to an image reproducing apparatus and, more particularly, to an image reproducing apparatus for correcting and reproducing nondecodable data of video signals encoded at high efficiency.
2. Description of the Related Art
An orthogonal transform coding method is known as a technique for compressing and expanding image signals at high efficiency. In this method, image signals are collectively formed into blocks, each block consisting of a predetermined number of pixels, and then an orthogonal transform, such as a discrete cosine transform, is performed so that quantization, entropy coding, and the like, are performed on coefficients after the transformation. In this method, since coding is performed in block units, when an error occurs in the coded data, the coding errors occur in block units. Also, since variable length codes are often used, decoding errors propagate over several blocks, resulting in significant deterioration of the image.
Hitherto, as means for correcting such error blocks by interpolation and obtaining reproduced images, inter-frame interpolation, wherein error blocks are replaced by using an image information from the preceeding frame has been utilized.
A correction operation using inter-frame interpolation is shown in FIG. 1. If block X of frame #n cannot be reproduced, inter-frame interpolation is performed by a method in which data of block X is replaced with reproduced data of block A, in the previous frame #n-1, at the same position on the screen, and the image is reproduced.
However, in such inter-frame interpolation, when the image moves violently from one frame to the next, interpolation data deviates, in terms of time, from the image data of the adjacent blocks within the same field, and the substituted data is completely different from the original image data. Therefore, when the data of the error block is replaced with the interpolation data, the resulting image may appear quite different from the way it should. It is also conceivable that image data in the same field may be used as interpolation data. In such a case, however, although there is a better correlation in terms of time, as compared with inter-frame interpolation, the correlation is decreased in terms of space, that is, using data from a different position on the screen but within the same field may cause the substituted data to be completely different from the original data.
Therefore, it is conceivable that the movement of blocks which cannot be reproduced may be estimated by using image data in the blocks above, below, to the left and to the right of the nonreproducible block, and the inter-frame and intra-field interpolations are switched in accordance with the movement of the image. In such a case, however, since the movement of the nonreproducible blocks is estimated by using only the upper, lower and the left and right blocks, it is likely to make an erroneous movement estimation, and there is a possibility that the interpolation will be performed using data having low correlation, contrary to what is desired.